Justin Bieber returned from Asia to find that re-entering the U.S. would not be easy.

The singer was detained at Los Angeles International Airport by U.S. Customs officials Thursday.

A source tells PEOPLE that Bieber was detained "for routine secondary questioning" but was not being kept out of the United States.

Bieber, 20, had reportedly been held for almost four hours inside Tom Bradley International Terminal after flying in from Tokyo while his entourage waited for him, but he was eventually released, according to E! News.